Bug 42705: Add HttpClient_spec.ts

This fails without the fix patch in this set:
cypress run --spec t/cypress/integration/HttpClient_spec.ts

It passes with the fix

Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>

Signed-off-by: Pedro Amorim <pedro.amorim@openfifth.co.uk>

t/cypress/integration/HttpClient_spec.ts

@@ -0,0 +1,29 @@
+describe("HttpClient", () => {
+    beforeEach(() => {
+        cy.login();
+        cy.title().should("eq", "Koha staff interface");
+    });
+
+    it("handles C4::Service error format without crashing", () => {
+        // C4::Service returns { type, message } on failure — not the OpenAPI
+        // { error } or { errors: [...] } shape that http-client.js was written for.
+        // Without the fix, accessing json.errors.map(...) throws:
+        //   TypeError: Cannot read properties of undefined (reading 'map')
+        cy.intercept("POST", "/cgi-bin/koha/svc/config/systempreferences", {
+            statusCode: 400,
+            headers: { "content-type": "application/json" },
+            body: { type: "auth", message: "expired" },
+        }).as("sysprefUpdate");
+
+        cy.window().then(win => {
+            const client = win.APIClient.sysprefs;
+            return client.sysprefs
+                .update("WebBasedSelfCheck", "1")
+                .catch(err => {
+                    expect(err.message).to.include("expired");
+                });
+        });
+
+        cy.wait("@sysprefUpdate");
+    });
+});